1. Field of the Invention
The present invention relates to a technique of drawing a pattern on a target object by radiating light from an optical head on the target object which relatively moves with respect to the optical head.
2. Description of the Background Art
In the following description, the “substrate” refers to, for example, a semiconductor substrate, printed substrate, a color filter substrate equipped in a liquid crystal display device, or a flat panel display (FPD) glass substrate of a liquid crystal display device, a plasma display device, or the like.
Although various exposure devices are conventionally proposed which performs various exposure processes with respect to substrates by radiating light on a substrate coated with a photosensitive material and drawing a pattern (exposure pattern) on the substrate, in recent years in particular, an exposure device (so-called direct drawing device) of a type which directly draws a pattern on a substrate from, for example, CAD data without using a photomask is getting an attention. The direct drawing device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-350034, Japanese Patent Application Laid-Open No. 3-89511 (1991), Japanese Patent Application Laid-Open No. 2001-176769, and Japanese Patent Application Laid-Open No. 2009-244446.
For example, the direct drawing device disclosed in Japanese Patent Application Laid-Open No. 2006-350034 spatially modulates light from a light source by controlling a DMD (Digital Micro-mirror Device) (registered trademark) which is a spatial modulator based on CAD data in which a pattern is described. Then, a pattern is drawn on the substrate by forming an image of spatially modulated light on the substrate.
Incidentally, the direct drawing device is demanded to precisely control a drawing position. When, for example, multiple exposure is performed, the next pattern must be drawn such that the next pattern is precisely overlaid on an existing pattern (underlying pattern) previously formed on the substrate.
However, although a thermal processing is applied thereafter to the substrate on which the underlying pattern is formed, after this thermal processing is performed, the substrate changes its shape due to distortion, shrinkage or expansion and therefore the underlying pattern formed on the substrate also changes due to the change of the shape. Further, when a different drawing device (exposure equipment) forms an underlying pattern, the underlying pattern also changes due to an instrumental error or precision. It is not easy to precisely overlay and draw the next pattern on the changed underlying pattern.
For example, Japanese Patent Application Laid-Open No. 2006-350034 discloses a technique of forming the next pattern at high overlaying precision in response to the change of an underlying pattern. This patent document discloses a configuration of detecting a position of an underlying pattern through a monitor before drawing a pattern, specifying the amount of position offset of the underlying pattern and correcting CAD data of the pattern which must be additionally formed according to the specified amount of position offset. According to this configuration, it is possible to draw a pattern such that the pattern is overlaid on the underlying pattern having a position offset by spatially modulating light from a light source using the corrected CAD data and forming an image of spatially modulated light on a substrate.
As described above, by applying the conventional technique of correcting CAD data of the pattern according to the amount of change of the underlying pattern, it is possible to draw a pattern such that the pattern is overlaid on the changed underlying pattern. Meanwhile, in this case, no matter how accurately CAD data is corrected, an actual drawing position is only corrected in pixel units of a spatial modulator. That is, it is fundamentally impossible to control a drawing position at precision subdivided more than a pixel size of the spatial modulator.